The long term objectives of this protocol proposal are to investigate the mechanisms and effect of pregnancy on glucose insulin sensitivity in women with normal glucose tolerance (NGT) and gestational diabetes(GDM). The specific aims are to :1) determine the relationship between the changes in glucose insulin sensitivity and level of expression of post receptor insulin signaling in skeletal muscle in lean and obese women with NGT and GDM in late gestation and post partum; 2) to determine the role of tumor necrosis factor alpha modulation of insulin receptor beta and insulin receptor substrate in skeletal muscle in late pregnancy and: 3) to characterize the effect of pregnancy on glucose metabolism.